Steering system with dynamic slip reduction

Abstract

A steering system includes a fluid motor and a steering unit. The steering unit is in fluid communication with the fluid motor. The steering unit includes a fluid meter adapted to meter fluid to the fluid motor in response to actuation of the steering unit. A valve housing is in fluid communication with the fluid meter. The valve housing defines a valve bore. A valve assembly is disposed in the valve bore. The valve assembly defines a primary fluid path to the fluid meter and to the fluid motor from the fluid meter. The valve assembly further defines a secondary fluid path to the fluid motor that bypasses the fluid meter. An amount of fluid through the secondary fluid path is based on volumetric efficiency of the fluid motor.

The invention claimed is: 
     
       1. A steering system configured for attachment to a steering wheel, the steering system comprising:
 a fluid motor; 
 a steering unit configured for receiving and expelling fluid; 
 wherein the steering unit is in fluid communication with the fluid motor, the steering unit including:
 a fluid meter configured to meter fluid to the fluid motor in response to actuation of the steering unit; 
 a valve housing in fluid communication with the fluid meter, the valve housing defining a valve bore; and 
 a valve assembly disposed in the valve bore and configured for receiving an input from the steering wheel; 
 wherein the valve assembly is moveable between a first open position and a second open position; 
 wherein the valve assembly defines a first variable orifice, a second variable orifice, a third variable orifice, and a fourth variable orifice on a primary fluid path to the fluid meter and to the fluid motor from the fluid meter; 
 wherein the valve assembly further defines the first variable orifice, the fourth variable orifice, and a bypass orifice on a secondary fluid path to the fluid motor, that bypasses the fluid meter; 
 wherein the valve assembly includes:
 a sleeve defining a bore; and 
 a spool disposed in the bore of the sleeve; 
 wherein the sleeve and the spool cooperate to define the bypass orifice; 
 wherein the sleeve and the spool extend about a central longitudinal axis and the spool is configured to rotate about the central longitudinal axis, relative to the sleeve, such that the spool is rotationally displaced, relative to the sleeve, about the central longitudinal axis in response to receiving input from the steering wheel; and 
 wherein the valve assembly moves between the first open position and the second open position in response to an amount of rotational displacement between the spool and the sleeve; 
 
 wherein the bypass orifice is open when the valve assembly is in the first open position such that the secondary fluid path is open and fluid is permitted to flow through each of the primary fluid path and the secondary fluid path; 
 wherein the amount of rotational displacement between the spool and the sleeve is less than or equal to 5 degrees when the valve assembly is in the first open position; 
 wherein the amount of rotational displacement between the spool and the sleeve is greater than 5 degrees when the valve assembly is in the second open position; 
 wherein fluid flows through the secondary fluid path in response to input from the steering wheel, as a function of a volumetric inefficiency of the fluid motor; and 
 wherein the bypass orifice is closed when the valve assembly is in the second open position such that the secondary fluid path is closed and fluid is permitted to flow through the primary fluid path and fluid is not permitted to flow through the secondary fluid path. 
 
 
     
     
       2. A steering system, as set forth in  claim 1 , wherein more fluid is permitted to flow through each of the first and fourth variable orifices when the valve assembly is in the second open position than when the valve assembly is in the first open position. 
     
     
       3. A steering system, as set forth in  claim 1 , wherein fluid is prevented from flowing through the secondary fluid path when there is no input from the steering wheel. 
     
     
       4. A steering wheel, as set forth in  claim 1 , wherein the bypass orifice is only in the open position when the amount of rotational displacement of the spool, relative to the sleeve, is between 3 degrees and 5 degrees. 
     
     
       5. A steering wheel, as set forth in  claim 4 , wherein the bypass orifice is only in the open position when the amount of rotational displacement of the spool, relative to the sleeve, is between 3.7 degrees and 5 degrees. 
     
     
       6. A steering unit configured for attachment to a steering wheel and configured to be in fluid communication with a fluid motor, the steering unit comprising:
 a fluid meter configured to meter fluid to the fluid motor in response to actuation of the steering unit; 
 a valve housing in fluid communication with the fluid meter, the valve housing defining a valve bore; 
 a valve assembly disposed in the valve bore and configured for receiving an input from the steering wheel; 
 wherein the valve assembly defines a primary fluid path to the fluid meter and to the fluid motor from the fluid meter; 
 wherein the valve assembly further defines a secondary fluid path to the fluid motor that bypasses the fluid meter, the valve assembly including:
 a sleeve including an inner surface opposing an outer surface, wherein the inner surface defines a bore extending along a central longitudinal axis; 
 wherein the sleeve defines:
 a bypass opening; 
 a first control opening and a second control opening, axially spaced from the first control opening; 
 a first meter port and a second meter port; and 
 an inlet opening; 
 wherein the bypass opening is axially disposed between the second control opening and the first and second meter port; 
 
 a spool disposed in the bore of the sleeve and configured to be rotationally displaced relative to the sleeve about the central longitudinal axis to move between a closed position, a first open position, and a second open position in response to input from the steering wheel; 
 wherein the spool defines:
 an inlet slot and a bypass passage; 
 a first annular groove and a second annular groove; and 
 a first control slot in fluid communication with the second annular groove; 
 wherein the first control slot of the spool is configured to provide fluid communication between the second meter port of the sleeve and the first and second control openings of the sleeve when the spool is rotationally displaced, relative to the sleeve; 
 
 wherein the spool cooperates with the sleeve to define a first and a fourth variable orifice when the spool is in the first open position; 
 wherein the bypass opening of the sleeve overlaps with the inlet slot and the bypass passage to define a bypass orifice located on the secondary fluid path when the spool is in the first open position such that fluid flows through the secondary fluid path to the fluid motor, via the first variable orifice, the fourth variable orifice, and the bypass orifice as a function of a volumetric inefficiency of the fluid motor; 
 wherein the bypass orifice is operatively disposed downstream of the first variable orifice and operatively disposed upstream of the fourth variable orifice such that fluid is prevented from being communicated to the fluid motor prior to input from the steering wheel; and 
 wherein fluid is prevented from flowing through the secondary fluid path to the fluid motor when the spool is not in the first open position. 
 
 
     
     
       7. A steering unit, as set forth in  claim 6 , wherein the spool further defines a second control slot in fluid communication with the first and second control openings of the sleeve when one of the first and second control openings of the sleeve are radially aligned with the second control slots of the spool when the spool is rotationally displaced relative to the sleeve. 
     
     
       8. A steering unit, as set forth in  claim 7 , wherein the valve assembly further defines a second and a third variable orifice;
 wherein the first variable orifice is defined by an overlap between the inlet opening of the sleeve and the inlet slot of the spool; 
 wherein the second variable orifice is defined by an overlap between the inlet slot of the spool and the first meter port of the sleeve; 
 wherein the third variable orifice is defined by an overlap between the second meter port defined in the sleeve and the first control slot defined in the spool; 
 wherein the fourth variable orifice is defined by an overlap between the first control slot defined in the spool and one of the first and second plurality of control openings defined in the sleeve. 
 
     
     
       9. A steering unit, as set forth in  claim 8 , wherein the spool is configured to be rotationally displaced relative to the sleeve about the central longitudinal axis to move between the closed position, the first open position, and the second open position in response to input from the steering wheel;
 wherein fluid flows through the first variable orifice, the bypass orifice, and the fourth variable orifice to the fluid motor when the spool is in the first open position; and 
 wherein fluid flows through the first, second, third, and fourth variable orifices to the fluid motor when the spool is in the second open position. 
 
     
     
       10. A steering unit, as set forth in  claim 9 , wherein the bypass orifice is in the first open position when the rotational displacement of the spool, relative to the sleeve, is less than or equal to 5 degrees; and
 wherein the first, second, and third variable orifices are only in the second open position when the rotational displacement of the spool, relative to the sleeve, is greater than 5 degrees. 
 
     
     
       11. A steering unit, as set forth in  claim 9 , wherein more fluid is permitted to flow through each of the first and fourth variable orifices when the valve assembly is in the second open position than when the valve assembly is in the first open position. 
     
     
       12. A steering unit, as set forth in  claim 8 , wherein the valve housing defines a first, a second, a third, and a fourth groove in fluid communication with the valve bore;
 wherein the first groove is configured to be in fluid communication with the inlet groove of the sleeve such that fluid flows from the first groove and into the sleeve; 
 wherein the second groove is configured to be in fluid communication with the outlet groove of the sleeve such that fluid flows from the outlet groove and into the second groove; 
 wherein the third groove is configured to be in fluid communication with the first control opening of the sleeve such that fluid flows from the first control opening and into the fluid motor; and 
 wherein the fourth groove is configured to be in fluid communication with the second control opening of the sleeve such that fluid flows from the fluid motor and into the first control opening. 
 
     
     
       13. A steering system configured for attachment to a steering wheel, the steering system comprising:
 a fluid motor; 
 a steering unit configured for receiving and expelling fluid; 
 wherein the steering unit is in fluid communication with the fluid motor, the steering unit including:
 a fluid meter configured to meter fluid to the fluid motor in response to actuation of the steering unit; 
 a valve housing in fluid communication with the fluid meter, the valve housing defining a valve bore; and 
 a valve assembly disposed in the valve bore and defining first, second, third, and fourth variable orifices and further defining a bypass orifice; 
 wherein the valve assembly defines a primary fluid path and a secondary fluid path and is movable in response to input from the steering wheel between a closed position, a first open position, and a second open position; 
 wherein the valve assembly includes:
 a sleeve defining a bore; and 
 a spool disposed in the bore of the sleeve; 
 wherein the sleeve and the spool cooperate to define the bypass orifice; 
 wherein the sleeve and the spool extend about a central longitudinal axis and the spool is configured to rotate about the central longitudinal axis, relative to the sleeve, such that the spool is rotationally displaced, relative to the sleeve, about the central longitudinal axis in response to receiving input from the steering wheel; 
 
 wherein the valve assembly moves between the first open position and the second open position in response to an amount of rotational displacement between the spool and the sleeve; 
 wherein the fluid meter and the second and third variable orifices are disposed on the primary fluid path, between the first and fourth variable orifices; 
 wherein the bypass orifice is disposed on the secondary fluid path, between the first and fourth variable orifices; 
 wherein the bypass orifice closed, such that fluid is prevented from flowing through the bypass orifice and through the secondary fluid path, when the valve assembly is in the second open position; 
 wherein fluid flows through the second variable orifice, the fluid meter, and the third variable orifice, via the primary fluid path to the fluid motor, when the valve assembly is in the second open position; 
 wherein the bypass orifice is open to allow fluid to flow therethrough, via the secondary fluid path to the fluid motor, when the valve assembly is in the first open position, as a function of a volumetric inefficiency of the fluid motor, such that the fluid meter is bypassed; 
 wherein the amount of rotational displacement between the spool and the sleeve is less than or equal to 5 degrees when the valve assembly is in the first open position; and 
 wherein the amount of rotational displacement between the spool and the sleeve is greater than 5 degrees when the valve assembly is in the second open position.